Composite structures are used in a wide variety of applications. In aircraft construction, composites are used in increasing quantities to form the fuselage, wings, and other components of the aircraft. The wings of an aircraft are generally hollow structures that may require a smooth and dimensionally-accurate outer mold line (OML) surface. The wings may be constructed of composite skin members and may include internal components such as ribs, spars, and/or stiffeners to increase the strength and bending stiffness of the wings.
In conventional construction techniques for forming three-dimensional composite structures such as an aircraft wing, cured composite components such as wing spars may be assembled to composite skin members by mechanical fastening. The process of assembling the composite components may require the use of a large quantity of mechanical fasteners and specialized tooling for maintaining the relative positions of the composite components during assembly. Unfortunately, the process of forming the cured composite components in a separate step and then later assembling such components using mechanical fasteners is a time-consuming and labor-intensive process. In addition, the mechanical fasteners may increase the overall weight of the composite structure. Furthermore, mechanical fasteners that are installed in OML surfaces may disrupt the aerodynamics of the composite structure.
Conventional processes for forming hollow composite structures also include the use of internal tooling. For composite structures having non-draftable geometry, the internal tooling must be removable from the interior of the composite part after curing. An inflatable mandrel may be installed within a hollow composite layup that may be positioned within a closed female mold. The inflatable mandrel may be inflated to apply an internal compaction pressure on the composite layup against the female mold to consolidate the composite layup. Heat may be applied to cure the composite layup. After curing of the composite layup, the mandrel may be deflated and removed from the cured composite structure. Unfortunately, an inflatable mandrel is generally limited in the ability to form the part surface geometry to a high level of accuracy. In addition, inflatable mandrels may be limited in their use with composite materials having high processing temperatures.
As can be seen, there exists a need in the art for a system and method for forming hollow, non-draftable, composite structures to a high level of accuracy and without the need for assembling composite parts using mechanical fasteners. Ideally, the composite forming system and method is relatively simple and includes reusable tooling that is durable to provide a relatively long useful life.